This invention relates to rotating apparatus for performing downhole operations in a wellbore, and more particularly to a slow rotating apparatus having a gear reducer.
There are a number of instances where a downhole apparatus having the capability of slow rotation at the end thereof is useful for performing a variety of different downhole operations. One primary use for such an apparatus is to remove the buildup of material on the inside of the pipelines, well casing or tubing. Unless removed, such buildup can plug tubing in both production and injection wells. Pipelines have similar problems. As set forth in U.S. Pat. No. 5,484,016 (the ""016 patent) issued Jan. 16, 1996 to Surjaatmadja et al. and U. S. Pat. No. 5,533,571 (the ""571 patent) issued Jul. 9, 1996 to Surjaatmadja et al., the details of both of which are incorporated herein by reference, there are a number of common compounds which cause buildup problems. Those compounds include barium sulfate, silicates, calcium carbonate, calcium sulfate, carbonate, sulfate, silica, water scale with hydrocarbons, coke tar, coke and complexes, wax and complexes, paraffin, sludges, muds and gels.
There are a number of different methods that have been used to remove material buildup. For example, paraffin buildup may be dealt with by utilizing hot oil to melt the paraffin. Hot water has also been used to melt or remove paraffin and chemicals are also utilized to dissolve paraffin deposits. Other methods to remove buildup include Dyna-Drills run on coil tubing, milling with jointed tubing, acid washing, and broaching with a wireline.
As noted in the ""016 patent, all of the above methods have certain deficiencies. To avoid the problems faced when applying such methods, jet cleaning was developed to utilize high-pressure liquids to remove the materials by erosion. Generally, jet cleaning has been limited to removing mud cake, paraffin or packed sand. Jet cleaning tools of the type used to perform such operations are usually made of heavy wall mechanical tubing with a plurality of holes of various diameters drilled in a symmetrical pattern around the tool. Water is used as the cleaning media. Job results were usually unpredictable. All of these techniques have achieved limited success, and it has been necessary on many occasions to change out the production tubing string. Accordingly, there is a need to efficiently and thoroughly clean material buildup in well casing or tubing.
The Otis xe2x80x9cHYDRA-BLASTxe2x80x9d(copyright) system was developed to address these problems by providing an economical means of cleaning buildup deposits from downhole tubing. This system utilizes high-pressure fluid jet technology in conjunction with the economy and efficiency of coiled tubing. The HYDRA-BLAST(copyright) system includes an indexing jet cleaning tool, an in-line high-pressure filter, a surface filter unit, a circulation pump with tanks and a coiled tubing unit. It also utilizes a computer program to design the actual cleaning jobs for any particular situation. The optimum jet size and number, retrieval speed and number of passes is calculated to accomplish a successful job, and this is particularly important in trying to remove harder materials such as the harder barium compounds. In general, this system may be described as a water-blasting system which directs high-pressure streams of water against the buildup to remove the material by the roding or cutting action of moving fluid.
In a typical application of the xe2x80x9cHYDRA-BLASTxe2x80x9d(copyright) system, the operator uses a cleaning tool which usually utilizes a downward stream to cut into the material as the tool is lowered into the tubing. This portion of the tool is not particularly well adapted for removing large amounts of buildup along the walls after the tool is free to pass therein. So, the original down-blast tool is removed from the well, and an additional trip is made with a side-blast jetting head designed specifically for the purpose of providing jets directed against the buildup on the walls of the tubing. Reciprocation of the tool is usually necessary for thorough cleaning. This two-step process works well for short or moderate length buildup areas, but it is not particularly well adapted for extremely long buildup areas because it is difficult to rotate and reciprocate the tool to cover such an area. Also, without the ability to rotate, a large number of nozzles will be needed to provide good coverage which will increase flow and pressure drop due to fluid friction. This reduces the efficiency of the jets.
The inventions set forth in the ""571 and ""016 patents address many of the deficiencies of prior art methods of removing buildup by providing a slow rotating mole apparatus for use in wellbores and pipelines but still has certain limitations. The invention described in the ""571 patent provides a method and apparatus for cleaning that generally does not require an additional trip into the wellbore. However, the ""571 patent is not directed to rotating apparatus. The invention described in the ""016 patent includes a speed reducer to provide a slow rotating jetting head. The speed reducer utilizes wobble gears so that the gears are tilted slightly with respect to the longitudinal axis of the entire apparatus. The wobble gear rotates and wobbles, thus causing a rotation and wobbling of jetting section. Because of the wobble gear, the apparatus described in the ""016 patent would not be usefull in applications where pure rotation is required.
For example, such an arrangement could not be effectively used where it was desired to utilize a fishing tool to thread into debris stuck in a wellbore to remove the debris therefrom. Likewise, the arrangement shown in the ""016 patent would not be useful if it were desired to cut tubing in a wellbore as opposed to simply removing debris therefrom. In addition, because of the wobbling motion of the follower gear described in the ""016 patent, the follower gear does not seal effectively with the body that houses the geared surfaces. Therefore, fluid from the wellbore, along with small grains of sand and other debris sometimes passes into the body and contaminates the body. Sand or other debris that enters the body can damage the gears and cause premature failure of the apparatus. The need therefore exists for a downhole apparatus which provides slow rotation with no wobble, which can be used, for example, to cut tubing or pipe in a wellbore, to blast and clean an area of buildup with only one trip into the wellbore, and to thread into the debris to remove debris from the wellbore. The need also exists for a slow rotating downhole tool that provides an effective seal as the tool is rotated.
The rotating apparatus of the present invention meets the above needs by providing a tool which translates high-speed motor rotation into slow output rotation. A seal is provided to prevent wellbore fluid from contaminating the interior of the apparatus and the apparatus can be rotated as it is lowered into the tubing to provide a complete 360xc2x0 path of jetted fluid as it is moved longitudinally in the tubing. If desired, the tool can be utilized as a cutting tool simply by holding the tool at one location and providing orizontal jetting ports in a jetting section.
The present invention comprises a slow rotating apparatus for use in downhole operations such as removing debris from wellbores and pipelines, cutting tubing or other pipe in wellbores and performing fishing operations.
The slow rotating apparatus has a motor section which provides rotation. A speed reducer section is connected to the motor section such that an output speed of the speed reducer section is less than an output speed of the motor. A jetting section may be attached to the speed reducer section. The jetting section has at least one jetting port through which said fluid is jetted in communication with a flow passage in the speed reducer.
The motor may comprise a progressive cavity motor having a rotor rotatably disposed in an elastomeric stator. A coupling may be used to connect the rotor and input shaft of the speed reducer section. The speed reducer section preferably comprises a rotatable input shaft which has an eccentric portion, and an input gear rotatably disposed about the input shaft on the eccentric portion thereof The input gear is a solid gear having first and second outer geared surfaces defined thereon. The second outer geared surface preferably has a smaller pitch diameter than the first outer geared surface. The second outer geared surface may have a larger pitch diameter than the first outer geared surface, but such an arrangement will reverse the direction of the output relative to the input.
The speed reducer section also comprises an inner geared surface defined on a speed reducer body which houses the input shaft. The first outer geared surface of the input gear is disposed in and is in geared engagement with the inner geared surface defined by the speed reducer body. A follower gear is disposed in the body about the input gear and is in geared engagement with the second outer geared surface of the input gear. The follower gear is rotatably disposed in the speed reducer body and is concentric with and thus shares the longitudinal central axis of the input shaft. Because the input gear is disposed about the eccentric portion of the input shaft, the gear will rotate eccentrically in the speed reducer body as the input shaft rotates about its longitudinal central axis. Clockwise rotation of the input shaft will cause the input gear to rotate eccentrically counterclockwise about the longitudinal central axis of the input shaft in the geared inner surface of the speed reducer body.
The eccentric rotation of the second outer geared surface in the follower gear will cause the follower gear to rotate in the speed reducer body at a rotational speed less than the rotational speed of the rotor. An output shaft is connected to and is rotatable by the follower gear. A jetting head or other desired head may be attached to the output shaft to perform downhole operations such as cleaning debris, cutting and other desired operations.
Numerous objects and advantages of the invention will become apparent as the following detailed description of the preferred embodiments is read in conjunction with the drawings which illustrate the embodiments.